1. Field of the Invention
The present invention relates to a pneumatic tire with an improved belt structure being capable of reducing the tire weight without sacrificing the steering stability, ride comfort, durability and the like.
2. Description of Related Art
In pneumatic tires especially radial tires, a tread reinforcing belt, which is composed of cords each made of twisted steel filaments, is widely used.
In recent years, on the other hand, there is a great demand for a lightweight tire to save energy.
In order to reduce the amount of steel in a tread reinforcing belt, a trial has been made using a relatively thick steel filament as a cord because such a monofilament cord has a less amount of steel than a multifilament cord when the bending rigidity of the monofilament cord is set at the same degree as the multifilament cord. However, the elongation of such a monofilament cord when loaded is very small and liable to break. Thus, the durability of the belt is not good, and the cornering force becomes insufficient and the steering stability is lowered. If the thickness is increased in order to avoid breaking, the bending rigidity suddenly increases, and ride comfort is greatly decreased. Thus, it is very difficult to use a monofilament cord in a tread reinforcing belt.